Back when I was shooting 16's a lot, I tried the 20ga SpredR inserts as well as the 16's. 16's sometimes gave almost too much spread, leaving a weak center. 20's didn't spread as much as I wanted. In addition to the shot on top of the insert, Jay Menefee used to--and maybe still does--include another method for modifying the inserts to give good spread but improve center density: punching holes in the insert. I experimented with a paper punch, cutting out 3 little semicircles around the periphery of the insert. Found that those modified inserts produced patterns I liked better than both unmodified 16ga inserts or 20ga inserts in a 16.
